Although FITC reagents have been more often used to prepare fluoresceinated bioconjugates, the low stability of FITC bioconjugates makes some researchers use amine-reactive succinimidyl esters of carboxyfluorescein (commonly called FAM) in bioconjugations. FAM reagents give carboxamides that are more resistant to hydrolysis. We have shown that FAM reagents require less stringent reaction conditions and give better conjugation yields, and the resulted conjugates have superior stability. We noted that FITC labeled peptides tend to deteriorate more quickly than the corresponding FAM conjugates.